1. Field of the Invention
The present invention relates to an emulsified external treatment composition containing diclofenac sodium and having an excellent stability.
2. Description of the Related Art
Diclofenac sodium is an excellent nonsteroidal antiphlogistic analgesic in the form of white crystals or a crystalline powder, is soluble in an alcoholic solvent such as methanol or ethanol, but is not easily solubilized in a polar oil such as ether, chloroform, diethyl phthalate, diethyl adipate, diisopropyl adipate, and diethyl sebacate. Accordingly, as the method of using diclofenac sodium in an external treatment agent, since it is soluble in an alcohol, there is known a gel preparation as in the case of indomethacin (Japanese Unexamined Patent Publication (Kokai) No. 59-76013) or an oily ointment having an improved solubility in an oily base by using a dissolving aid such as propylene glycol, (Japanese Unexamined Patent Publication (Kokai) No. 59-33211). Also, O/W type emulsion bases have been developed (Progress in Medicine, Vol. 4, 1411-1413, 1984), but have a problem of stability of the pharmaceutical preparation, and a satisfactory emulsion base has not been obtained.
When an emulsified external treatment agent containing diclofenac sodium is prepared, it is very difficult to effect emulsification, because diclofenac sodium, although slightly soluble in water, is substantially not soluble in diethyl adipate or diethyl sebacate, and even if emulsification is effected by dissolving it in water while heating, a drawback arises in that diclofenac sodium crystals will be precipitated after a certain time. Although the development of an emulsion base having an excellent texture is desired, an emulsified external treatment agent stably containing diclofenac sodium is not known to date.